The invention relates to an arrangement for bearing relief in a gas turbine, especially for reducing the axial forces that act on the high-pressure bearing in an aircraft gas turbine comprising a blade cooling chamber formed between the compressor and the high-pressure turbine along the high-pressure shaft and supplied with compressor air.
It is known that the compressor in aircraft gas turbines generates a load in flight direction while the load originating from the turbine acts in opposite direction. The compressor load is typically greater than the turbine load on the high-pressure shaft of an aircraft gas turbine. The difference between the two opposite forces acts on the respective locating bearing (high-pressure bearing). The load on the locating bearing is the greater the more the forces emerging from the compressor and from the turbine deviate. As the design of gas turbines is improved to achieve higher ratings, process pressures, temperatures and speeds are increased which eventually increase the axial loads acting on the high-pressure bearing. The known solid metal bearings reach speed limits as a result of high centrifugal forces. The known hybrid bearings can be used at higher speeds but cannot absorb higher loads. The bearing problems resulting from increased load on bearings require shorter maintenance intervals or reduce the service life of the bearings. This sets tight limits for improving the power density of gas turbines.
In stationary turbines, the problem of bearing load compensation is known especially from high-performance turbines. The forward force of the fan is missing on the low-pressure shaft of stationary turbines derived from aircraft turbines. Such turbines are therefore equipped with additional devices that perform bearing load compensation. These devices can be located outside the gas turbine, which is not easily feasible with a high-pressure shaft.
The load acting on the low-pressure bearing in an industrial gas turbine known from U.S. Pat. No. 573,566 is reduced by constructional measures that can only be located outside the stationary gas turbine. An aircraft gas turbine is not suited for external constructional modifications.
U.S. Pat. No. 4,864,810 describes a steam piston balancing system for reducing the compressor forces that act on an axial bearing. To at least partially reduce the axial backward force that acts on the locating bearing, a pressure chamber supplied with vapor that comprises an inner surface that is connected with the bearing and rotates with it, is provided inside the gas turbine. An axial forward compressive force applied to the inner surface is transmitted to the locating bearing to provide relief. This type of bearing load reduction comes with the disadvantage that it requires the design of a pressure chamber and the provision of a high-pressure vapor source for controllable application of pressure to the inner surface of the pressure chamber that rotates with the locating bearing.
It is the problem of this invention to provide an internal arrangement in a gas turbine for reducing the differential force acting from the compressor and the turbine on a locating bearing that is of simple design and enables controlled bearing relief.